The present invention relates in general to x-ray systems and in particular to a system for initiating automatic exposure in a digital CCD camera x-ray imager.
In conventional x-ray imaging a photographic film is exposed to visible light in order to capture the image of the object being x-rayed. The x-rays are passed through the object and impinge on an imaging screen, such as a phosphor imaging screen. The phosphor imaging screen converts some of the radiation into a selected spectral component (typically visible light). The exposure of the photographic film to the spectral component from the phosphor imaging screen produces the image of the object on the photographic film.
Recent advances in x-ray imaging however have changed the focus from use of photographic films to electronic imaging sensors. Such a system is disclosed in U.S. Pat. No. 5,309,496, entitled xe2x80x9cFILMLESS X-RAY APPARATUS AND METHOD OF USING THE SAMExe2x80x9d, issued to Winsor, which is hereby incorporated herein by reference. In the preferred embodiment of Winsor, a video camera and a frame grabber are used to provide still x-ray images. Winsor uses a photocell detector near the imaging screen to detect the burst of visible light. The photocell would activate the frame grabber upon detecting light, thereby capturing the image on the imaging screen.
Another sensor is a photo multiplier tube (PMT) sensor. This type of sensor converts photons into electrons and through a cascade effect, accelerates the electrons to generate more electrons. This sensor also would measure light coming from the phosphor imaging screen, from the stimulation by the x-rays, and would trigger the camera to acquire the image.
Both types of sensor suffer from the same problem, namely false signaling. The false signal would originate from ambient noise or line noise, e.g. input power supply spikes. Consequently, the camera would be receiving incorrect triggering signals, creating premature imaging. The noise could be any kind of interference that would have a voltage that exceeds the threshold voltage of the sensor.
Therefore, there is a need in the art for an automatic exposure initiator which does not trigger on false signals, and triggers on actual signals.
These and other objects, features and technical advantages are achieved by a system and method which uses a visible light sensor and a signal detector with integral noise filtering.
The present inventive system comprises a lead (pb) shielded PMT (Photo-Multiplier Tube) as the sensor, which is mounted at right angles to the light/x-ray source and facing with a reflective surface to capture the light, and an AEI PCB (Automatic Exposure Indicator Printed Circuit Board) to provide noise filtering and signal detection. When the PMT detects light for a sufficient duration and intensity in the right wavelength, it generates a signal and outputs it to the board. Any noise in the light signal is filtered out or ignored by the board. Thus, board detects the signal, ignores the noise and initiates the exposure sequence in the digital CCD cameras. The board measures the signal over time, and for a signal to be an accurate signal, each measurement of the signal needs to be higher (in voltage) than the preceding measurement, otherwise the signal is rejected as noise.
Accordingly, it is a technical advantage of the present invention to provide a high resolution digital x-ray imaging system.
It is another technical advantage of the present invention to provide trigger signal to the camera of the imaging system when a light sensor a detects light from the imaging screen.
It is still another technical advantage of the present invention to filter out noise from the light signal from the sensor, and thereby prevent erroneous images.
It is a further technical advantage of the present invention filter noise from a negative going signal or a spike of a short duration from the light signal.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.